Focal adhesion kinase signaling pathway participates in the formation of choroidal neovascularization and regulates the proliferation and migration of choroidal microvascular endothelial cells by acting through HIF-1 and VEGF expression in RPE cells

Abstract

Choroidal neovascularization (CNV) is one of the most frequent causes of severe and progressive vision loss, while its pathogenesis is still poorly understood. Focal adhesion kinase (FAK), a non-receptor tyrosine kinase, plays a crucial role in linking signals initiated by both the extracellular matrix (ECM) and soluble signaling factors and controls essential cellular processes. Extensive evidence has shown that FAK is activated in angiogenic response. This study aims to investigate the effect of FAK on CNV formation. The Brown-Norway (BN) rats underwent laser rupture of Bruch's membrane to induce CNV and were then killed at 1, 3, 7, and 14 days following laser injury. Immunofluorescence and Western blot were processed to detect FAK protein. Retinal pigment epithelial (RPE) cells were cultured under hypoxia and RNA interference (RNAi) technique was used to knock down the FAK gene in RPE cells. Expression of hypoxia inducible factor-1 (HIF-1alpha) and vascular endothelial growth factor (VEGF) in RPE cells were investigated by RT-PCR and Western blot. Two kinds of coculture models were used to observe the effects of specific blockade of FAK in RPE cells on the proliferation and migration of choroidal microvascular endothelial cells (CECs), respectively. FAK was highly expressed in the rat RPE-choroid tissue after photocoagulation. In vitro experiment showed that FAK was involved in hypoxia signaling in cultured RPE cells. The absence of FAK effectively reduced the expression of hypoxia-induced HIF-1alpha and VEGF in RPE cells, resulting in the inhibition of proliferation and migration of CECs. Our results suggest that FAK pathway activation plays a role in the development of CNV, and regulates the proliferation and migration of CECs by acting through HIF-1 and then up-regulating the expression of the angiogenic factor VEGF in RPE cells. It is reasonable to propose that FAK siRNA will potentially provides a means to attenuate the strong stimuli for neovascularization in CNV-dependent disorders, which could present a therapeutically relevant strategy for the inhibition of CNV.